Hi. I'm an unmarried woman in her forties. I use Ms. and pronounce it "miz", though I don't correct people who accidentally use a soft S. I use Ms. because it's no one's business but my own whether I'm married, to a man or anyone else, and that's what Ms. means. It means fuck off, my marital status is irrelevant, just as it is for every man who uses Mr.
I've had people (usually children) ask me at work if I'm a missus or a miss. I have replied that I am a miz, full stop. And when they pressed for which one I was REALLY, I have replied, "Why? Are you going to treat me differently depending on whether there's a ring somewhere?"
That's what Ms. is for. That is its linguistic function. It says, "This is an adult woman," and nothing else. Nothing else is necessary, and in my case, nothing else is desired.
I also use miz for other women unless and until they express a preference for something else because I don't magically know everyone else's marital status when I meet them. That's a courtesy—I'm declining to assume marital status and allowing them to decide whether they wish to declare it.
Also, I've taught English and worked as an editor for twenty years. I am quite literally the grammar police. This use of Ms. is a standard construction. If you didn't learn it in school, someone failed you.